The present invention relates to remote metering and in particular to radio frequency transmitters suitable for remote metering applications.
Public and private utility distribution companies, for example water, gas and electricity distributors, are continuously exploring new ways to monitor service provision and to reduce costs. Increasing the number of times that readings from a particular meter are taken can improve the monitoring of the service. However, increased readings with current manual systems would result in higher costs due to the increased number of meter reading personnel that would be required.
Thus, it is desirable to provide utility meters, which can be remotely accessed, for example by way of a radio frequency (RF) communication system.
A previously considered remote metering system is shown schematically in FIG. 1, and comprises a number of remote meters 1 which communicate in groups to remote metering concentrators 2. The remote metering concentrators 2 are in turn connected to communicate with a central billing unit 3. In such systems, the remote meters 1 may ideally communicate with a remote meter concentrator 2 by way of a radio frequency communications link. The concentrators 2 can communicate with a gateway to the central billing unit 3 by way of a radio frequency link, a PSTN land line, or other wide area network.
One way of avoiding signal clash between remote units in the same group would be to provide a distinct channel for each remote meter in the group. This however would prove extremely costly, both in terms of money and bandwidth requirements. Reducing the number of remote meters in a group would decrease the number of channels required, but would mean that many more concentrators would be required, hence increasing the cost.
However, there is a problem associated with using radio frequency communications for such metering applications, because of the large number of meters involved, particularly in cities. Such large numbers of meters can easily lead to collision of the signals from adjacent meters, and hence lead to loss of data.
Previously considered systems have incorporated radio connections in which polling of remote meters takes place by the concentrator. The concentrator polls the meter to request information, and in reply the meter concerned returns the meter reading. This requires a complicated receiver and decoder to be provided in each meter.
According to a first aspect of the present invention, there is provided a meter for use in a radio frequency remote metering system, the meter comprising a transmitter for transmitting meter signals, a receiver for receiving and filtering an incoming radio frequency signal, and a carrier signal detection circuit, which is connected to receive the filtered radio frequency signal and which is operable to detect the presence or absence of a carrier signal, and to prevent activation of the transmitter in response to the presence of the carrier signal, and to activate the transmitter in response to the absence of the said carrier signal.
Preferably, the receiver can be provided with a local oscillator signal by the transmitter, and the transmitter output can be isolated from its antenna. The local oscillator frequency is preferably set differently to that required by the transmitter for transmission of a signal.
In one embodiment of the present invention, meter information is stored in a non-volatile memory. In an electricity meter embodying the present invention, the mains supply lines can provide the power supply for the meter.
According to a second aspect of the present invention, there is provided a remote metering system comprising a plurality of meter according to the first aspect of the invention, at least one remote meter concentrator for receiving signals from a predefined group of remote meters, and a central control unit for receiving signals from each remote meter concentrator.
The data from the meters is maintained at the concentrator, reducing the data traffic from the meters when a request for a reading comes from the utility. This is particularly necessary where the country regulations require a 20%/80% data flow on the license exempt frequency allocation between meters and concentrators.
Thus aspects of the present invention do not need to perform the process of poll, request and reply associated with previously considered systems.
Another problem associated with remote metering devices is the desirably small size of the meter housing, so that the meter is unobtrusive. This restricts the size of the antenna, which in turn can restrict the effective propagation range between the transmitters and receivers.
According to a third aspect of the present invention, there is provided a radio frequency transmitter system for use in a metering device, wherein a supply line of the metering device serves as an antenna for the transmitter.
One electricity meter embodying the third aspect of the present invention makes use of the earth supply line as an antenna.
Thus, the third aspect of the invention can provide a longer antenna than previously available for small meter applications. This leads to consequent improvements in propagation and performance.